In combustion systems it is often desirable to obtain a combustion reaction having selected characteristics. For instance, it can be beneficial for a particular a combustion system to receive uniform heat over a particular volume, or for a portion of the combustion system to receive more heat than other parts of the combustion system—for example to tailor a heat flux profile along the process tubes of certain furnaces. Likewise, it can be beneficial for the combustion reaction to have a particular width, length, or temperature.